Production of mercaptan-terminated polymers

ABSTRACT

Polymers having mercaptan terminal groups are prepared by reacting a polymer-metal reactant with an aromatic thioketone to produce a polymer having improved vulcanizate properties.

United States Patent Uraneck et al.

[ Aug. 28, 1973 PRODUCTION OF MERCAPTAN-TERMINATED POLYMERS Inventors:Carl A. Uraneck; Richard L. Smith,

both of Bartlesville, Okla.

Assignee: Phillips Petroleum Company, Bartlesville, Okla.

Filed: Sept. 30, 1971 Appl. No.: 185,343

US. Cl 260/79.5 NV Int. Cl. C08f 27/06 Field of Search 260/795 C, 79.5NV,

Primary Examiner-Joseph L. Schofer Assistant Examiner-C. A. Henderson,Jr. Attorney-Young & Quigg [57] ABSTRACT Polymers having mercaptanterminal groups are prepared by reacting a polymer-metal reactant withan aromatic thioketone to produce a polymer having improved vulcanizateproperties.

10 Claims, No Drawings PRODUCTION OF MERCAP'IAN-TERMINATED POLYMERS Thisinvention relates to the production of mercaptan terminated polymers.

In one of its more specific aspects, this invention relates to theproduction of rubbery polymers having mercaptan terminal groups, thepolymers having superior vulcanizate properties when compounded intypical sulfur-based vulcanization systems. Such polymers, because oftheir superior vulcanizate properties, are peculiarly suitable forincorporation in rubber formulations. Previous attempts to prepare suchpolymers from polymers having terminal polymermetal groups by employingsulfur, cyclic disulfides and other sulfurcontaining substances,however, have been largely unsuccessful in that the mercaptan content ofthe polymer product has been less than theoretical because of sidereactions or coupling reactions occurring during polymer isolation.There has now been discovered a method of employing a reagent whichlargely avoids these problems and gives a product having close to thetheoretical mercaptan content. This invention presents that method andthe product produced therefrom.

According to this invention there is provided a method for producing apolymer which involves reacting a polymer-metal reactant with anaromatic thioketone to produce a polymer having improved vulcanizedproperties. The invention also concerns the polymers, themselves.

The method of this invention is applicable to polymers having thegeneral formula P(M) wherein P is a polymer as hereinafter defined, M isan alkali metal or an alkaline earth metal such as a metal selected fromGroup or Group of the Periodic Table as shown in the Handbook ofChemistry and Physics, Chemical Rubber Company, 46th Edition (1965),page B-3and x is an integer having a value of from I to 4.

The polymers referred to above include those prepared from monomers suchas conjugated dienes having from 4 to 12 carbon atoms per molecule, fromvinyl aromatic hydrocarbons having from 8 to 20 carbon atoms permolecule and from esters of acrylic and methacrylic acid,alpha-beta-unsaturated nitriles, vinyl pyridines and like substanceshaving from 3 to 20 carbon atoms per molecule. Preferred polymers areformed using l,3-butadiene, isoprene, 1,3-pentadiene, styrene,4-methylstyrene, 4-tertiary-butylstyrene, methyl methacrylate,arcylonitrile, methacrylonitrile, 2-vinylpyridine and the like.

Such polymers are formed by methods well known in the art, these methodsemploying monofunctional or multifunction orgaonmetal initiators or themetals themselves wherein the metal is selected from Groups la and 2a ofthe Periodic Table. Copolymers of two or more of the mentioned monomerscan be formed.

Particularly suitable polymers are polybutadiene and butadiene-styrenecopolymers, either having one or two lithium atoms per molecule, thesebeing prepared by polymerization initiated with organolithium compoundssuch as n-butyllithium or 1,6-dilithiohexane.

This invention contemplates the use of aromatic thioketones having thegeneral formula wherein X and X can be alike or different, both beingselected from the group consisting of hydrogen, alkyl, cycloalkyl,alkoxy and dialkylamino substituents. Generally, the total number ofcarbon atoms of the X groups or the X groups on either ring will notexceed 12.

Suitable aromatic thioketones include thiobenzophenone;4,4'-dimethyl-thiobenzophenone; 3 ,3 dicyclohexylthiobenzophenone;4,4'dimethoxythiobenzo-phenone; 4,4'-bis(dimethylamino)thiobenzophenone;4-methyl-4'-methoxythio-benzophenone; 4,4'-diethoxythiobenzophenone;2,2'-dimethoxythiobenzophenone; 3,4-dimethoxythiobenzophenone; 4-dimethylaminothiobenzophenone; and 2,2, 3 ,3'-tetramethylthiobenzophenone.

The aromatic thioketone or a mixture of such thioketones is employed inan amount within the range of from about 0.5 to about 4 moles perequivalent of metal in the polymer-metal reactant, P(M) The thioketoneand polymer metal reactant are reacted at a temperature within the rangeof about 0 to about 150 C. for a period of from 0.5 minutes up to about10 hours, preferably at a pressure which maintains the reactantssubstantially in the liquid phase.

Inasmuch as the polymer-metal reactant is usually prepared in thepresence of an inert hydrocarbon diluent, it is convenient to conductthe reaction with the aromatic thioketone in the presence of thisdiluent, introducing the aromatic thioketone into the polymerizationreaction mixture prior to shortstopping the polymerization reaction.

The reaction product of the polymer-metal reactant and the aromaticthioketone is recovered by conventional recovery procedures such ascoagulation or steam-stripping. Generally, it is not necessary toperform a separate hydrolysis step during the polymer recovery procedurefor the purpose of converting the S-M group to the 8-H group becausethis conversion takes place normally during steam-stripping orcoagulation with alcohol. An antioxidant can be added in the usualmanner to the reaction mixture prior to the polymer recovery.

It is desirable to avoid excessive loss of the 8-H functional groupduring recovery as a result of contact with oxygen or air. Similarly, itis desirable to avoid excessively high temperatures, such astemperatures above 300 F. in the recovery and drying of the polymer.

The following examples illustrate the method of this invention asapplied in the preparation of polybutadiene polymers andbutadiene/styrene polymers.

EXAMPLE I Polybutadiene-lithium products were produced by polymerizing100 parts by weight of 1,3-butadiene in the presence of 1,400 parts byweight of cyclohexane by 7 gram millimoles per 100 g of butadiene ofnbutyllithium at about C. for about 20 minutes.

Each polymerization reaction mixture prepared with the above recipeusing a 10 g monomer charge was reacted with either4,4-bis-(dimethylamino)thiobenzophenone (DMATB) orl,8-naphthalenedisulfide (NDS) for about 10 minutes at about 50 C.Certain of the resulting mixtures were then treated with 2 ml ofisopropyl alcohol (IPA) or 2 ml of acetic acid (HAC) to hydrolyze theP-S-Li species to P-S-I'I. Each mixture was then analyzed for -S-H or-S-Li'content. Then a stream of air was passed through each mixture for10 minutes at about 25 C. with analyses for S-l-l and S-Li beingconducted thereafter. Results were as follows:

DMAIB, NDS, HAG, IPA, mhm. mhm ml. m1. Initial Air exposed Run.

EXAMPLE ll Polymer A was prepared by polymerizing 1,3- butadiene andstyrene in cyclohexane employing a conventional prior art method. At theend of a defined polymerization period,4,4'-bis(dimethylamino)thiobenzophenone in an amount within the rangepreviously prescribed was added to the reaction mixture and allowed toreact at 50 C. for 10 minutes. An antioxidant was added and the polymerwas recovered. Upon analysis, the concentration of the -S-H group wasdetermined as 5.1 X 10 mmoles per gram of polymer as compared to atheoretical maximum of 8.5 X 10 mmoles per gram of polymer.

Polymer B was prepared according to a procedure substantially identicalto that used to prepare Polymer A except that no aromatic thioketone wasemployed in its production.

Both polymers were then individually incorporated in a rubbercompounding recipe conventionally employed in such comparative analyses,both compounded stocks being compounded, cured and tested insubstantially the identical manner. The results of those comparativetests are set forth below, the testing methods in each instance beingaccording to conventional ASTM procedures.

Polymer A B Raw Mooney Viscosity, ML-4 39.5 37 Compounded Mooney, ML-463.5 70 300% Modulus, psi i735 1645 Tensile, psi 3950 3960 Elongation,505 520 Heat Build-up, AT "F. 59 66.5 Resilience, 71.4 67.1 Shore AHardness 61.5 64.5

The above data indicate that Polymer A, the polymer produced by themethod of this invention, had significantly improved dynamic propertiessuch as heat buildup and resilience compared to Polymer B which wasproduced in the absence of the practice of this invention, while havingcomparable stress-strain properties. These data also indicate that themethod of this invention is applicable to both homopolymers andcopolymers.

It It will be evident that various modifications may be made to themethod of this invention. However, such are considered to be within thescope of the invention.

We claim:

1. A composition prepared by the process of reacting (a) ametal-terminated polymer having the general formula P(M) wherein P is apolymer prepared from a material selected from the group consisting ofconjugated dienes having 4 to 12 carbon atoms per molecule, vinylaromatic hydrocarbons having 8 to 20 carbon atoms per molecule, estersof acrylic acid and methacrylic acid, alpha,beta-unsaturated nitriles,and vinyl pyridines having 3 to 20 carbon atoms per molecule, M is analkali metal or an alkaline earth metal and x is an integer having avalue within the range of from 1 to 4, and (b) an aromatic thioketonehaving the formula X X' X X wherein X and X are selected from the groupconsisting of hydrogen, alkyl, cycloalkyl, alkoxy and dialkylaminoradicals, the total number of carbon atoms of said X and X on either ofthe benzene rings being not greater than 12.

2. The composition of claim 1 in which said metalterminated polymer is alithium-contained polybutadiene polymer.

3. The composition of claim 1 in which said metalterminated polymer is alithium-containing butadienestyrene polymer.

4. The composition of claim 1 in which said metalterminated polymer isformed from at least one material selected from the group consisting ofl,3-

butadiene, isoprene, 1,3-pentadiene, styrene, 4- methylstyrene,4-tertiary-butylstyrene methyl methacrylate, acrylonitrile,methacrylonitrile and 2- vinylpyridine.

5. The composition of claim 1 in which said aromatic thioketone isselected from the group consisting of thiobenzophenone;4,4-dimethylthio-benzophenone; 3 ,3- -dicyclohexylthiobenzophenone;4,4'-dimethoxythiobenzo-phenone; 4,4'-bis(dimethylamino)thiobenzophenone; 4-methyl-4-methoxythio-benzophenone;4,4'-diethoxythiobenzophenone; 2,2-dimethoxythiobenzophenone;3,4-dimethoxythiobenzophenone; 4- dimethylaminothiobenzophenone; and 2,2',3 ,3 tetramethylthiobenzophenone.

6. The composition of claim I in which said aromatic ketone is4,4-bis(dimethylamino)thiobenzophenone.

7. The composition of claim 2 in which said aromatic ketone is4,4-bis(dimethylamino)thiobenzophenone.

8. The composition of claim 3 in which said aromatic ketone is4,4-bis(dimethylamino)thiobenzophenone.

9. The composition of claim 1 in which said aromatic thioketone isreacted with said metal terminated polymer in an amount within the rangeof from about 0.5 to about 4 moles per equivalent of metal in saidmetalterminated polymer.

10. The composition of claim 8 in which said 4,4-bis(dimethylamino)-thiobenzophenone is reacted with saidlithium-containing butadiene-styrene polymer in an amount within therange of from about 0.5 to about 4 moles per equivalent of lithium insaid polymer.

2. The composition of claim 1 in which said metal-terminated polymer isa lithium-contained polybutadiene polymer.
 3. The composition of claim 1in which said metal-terminated polymer is a lithium-containingbutadiene-styrene polymer.
 4. The composition of claim 1 in which saidmetal-terminated polymer is formed from at least one material selectedfrom the group consisting of 1,3-butadiene, isoprene, 1,3-pentadiene,styrene, 4-methylstyrene, 4-tertiary-butylstyrene methyl methacrylate,acrylonitrile, methacrylonitrile and 2-vinylpyridine.
 5. The compositionof claim 1 in which said aromatic thioketone is sElected from the groupconsisting of thiobenzophenone; 4,4''-dimethylthio-benzophenone;3,3''-dicyclohexylthiobenzophenone; 4, 4''-dimethoxythiobenzo-phenone;4,4''-bis(dimethylamino)thiobenzophenone;4-methyl-4''-methoxythio-benzophenone; 4,4''-diethoxythiobenzophenone;2,2''-dimethoxythiobenzophenone; 3,4-dimethoxythiobenzophenone;4-dimethylaminothiobenzophenone; and2,2'',3,3''-tetramethylthiobenzophenone.
 6. The composition of claim 1in which said aromatic ketone is 4,4-bis(dimethylamino)thiobenzophenone.7. The composition of claim 2 in which said aromatic ketone is4,4-bis(dimethylamino)thiobenzophenone.
 8. The composition of claim 3 inwhich said aromatic ketone is 4,4-bis(dimethylamino)thiobenzophenone. 9.The composition of claim 1 in which said aromatic thioketone is reactedwith said metal terminated polymer in an amount within the range of fromabout 0.5 to about 4 moles per equivalent of metal in saidmetal-terminated polymer.
 10. The composition of claim 8 in which said4,4-bis(dimethylamino)-thiobenzophenone is reacted with saidlithium-containing butadiene-styrene polymer in an amount within therange of from about 0.5 to about 4 moles per equivalent of lithium insaid polymer.